1. Field of the Invention
This invention relates generally to a method for making monoclonal antibodies. The invention further pertains to antibodies obtainable by the method which specifically cross-react with two or more different receptors to which Apo-2 ligand (Apo-2L) can bind.
2. Description of Related Art
Native antibodies are synthesized primarily by specialized lymphocytes called "plasma cells". Production of a strong antibody response in a host animal is controlled by inducing and regulating the differentiation of B cells into these plasma cells. This differentiation involves virgin B cells (which have a modified antibody as a cell-surface antigen receptor and do not secrete antibodies) becoming activated B cells (which both secrete antibodies and have cell-surface antibodies), then plasma cells (which are highly specialized antibody factories with no surface antigen receptors). This differentiation process is influenced by the presence of antigen and by cellular communication between B cells and helper T cells.
Because of their ability to bind selectively to an antigen of interest, antibodies have been used widely for research, diagnostic and therapeutic applications. The potential uses for antibodies were expanded with the development of monoclonal antibodies. In contrast to polyclonal antiserum, which includes a mixture of antibodies directed against different epitopes, monoclonal antibodies are directed against a single determinant or epitope on the antigen and are homogeneous. Moreover, monoclonal antibodies can be produced in unlimited quantities.
The seminal work by Kohler and Milstein described the first method for obtaining hybridomas that can produce monoclonal antibodies [Kohler and Milstein Nature 256:495 (1975)]. In this method, an antibody-secreting immune cell, isolated from an immunized mouse, is fused with a myeloma cell, a type of B cell tumor. The resultant hybrid cells (i.e. hybridomas) can be maintained in vitro and continue to secrete antibodies with a defined specificity.
Since murine monoclonal antibodies are derived from mice, their use as therapeutic agents in humans is limited because of the human anti-mouse response that occurs upon administration of the murine antibody to a patient. Accordingly, researchers have engineered non-human antibodies to make them appear more human. Such engineered antibodies are called "chimeric" antibodies; in which a non-human antigen-binding domain is coupled to a human constant domain (Cabilly et al., U.S. Pat. No. 4,816,567). The isotype of the human constant domain may be selected to tailor the chimeric antibody for participation in antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity. In a further effort to resolve the antigen binding functions of antibodies and to minimize the use of heterologous sequences in human antibodies, Winter and colleagues [(Jones et al., Nature 321:522-525 (1986); Riechmann et al., Nature 332:323-327 (1988); Verhoeyen et al., Science 239:1534-1536 (1988)] have substituted rodent complementarity determining region (CDR) residues for the corresponding segments of a human antibody to generate humanized antibodies. As used herein, the term "humanized" antibody is an embodiment of chimeric antibodies wherein substantially less than an intact human variable domain has been substituted by the corresponding sequence from a non-human species. In practice, humanized antibodies are typically human antibodies in which CDR residues and possibly some framework region (FR) residues are substituted by residues from analogous sites in rodent antibodies.
Other groups have developed methods for making fully "human" monoclonal antibodies. Such antibodies may be generated by immortalizing a human cell secreting a specific antibody using an Epstein-Barr virus (EBV) [Steinitz et al. Nature 269:420-422 (1977)]; or by preparing a human--human hybridoma secreting the monoclonal antibody [Olsson et al. PNAS (USA) 77:5429-5431 (1980)]. Human antibodies can also be derived from phage-display libraries [Hoogenboom et al., J. Mol. Biol., 227:381 (1991); Marks et al., J. Mol. Biol., 222:581-597 (1992); Vaughan et al. Nature Biotech 14:309 (1996)].
Alternatively, human antibodies have been made in transgenic laboratory animals, in which human immunoglobulin loci have been introduced into the animal and the endogenous immunoglobulin genes are partially or completely inactivated [Fishwild et al. Nature Biotech. 14:845-851 (1996); and Mendez et al. Nature Genetics 15:146-156 (1997)].